Resin composition

ABSTRACT

The invention relates to a composition compriseing an at least bifunctional acidic prepolymer (A) curable under the action of heat an compound of the formula (I) in which A is a mono- to tetravalent, saturated or unsaturated alkyl group having 1 to 60 carbon atoms, a mono- to tetravalent aryl group, a mono- or diaiylamino group having 1 to 4 carbon atoms, an alkenylene group having 2 to 4 carbon atoms, a carboxyalkylene group or an alkoxycarbonylalkylene group having 1 to 4 carbon atoms, n is 1 or 2, m is 2-n, q is a number from 0 to 3, R 1  is hydrogen or an alkyl group having 1 to 5 carbon atoms or a hydroxyalkyl group having 1 to 5 carbon atoms and X is a radical of the formula in which R 3  and R 4  are identical or different and, independently of one another, are hydrogen, a straight-chain or branched alkyl group or hydroxyalkyl group having 1 to 5 carbon atoms, or R 3  and R 4 , together with the carbon atom to which they are bonded, form a cycloaliphatic ring. The composition is suitable for the production of printed circuits.

The invention relates to a resin composition and printed circuitscompriseing an optionally photostructured layer produced from this resincomposition.

In the production of printed circuits, a protective film is applied to aprinted circuit board in order to protect the electrical circuit and toprevent adhesion of solder material in undesired areas when electricalparts are being soldered onto the printed circuit board. The greatdemand for increasingly light circuit boards and the wish for a highdensity of circuits mean that the compositions have to have very goodadhesion properties, chemical stabilities and good electricalproperties.

Conventional heat-curable and photopolymerizable compositions frequentlycomprise an epoxy compound and a photosensitive prepolymer. If such acomposition is developed in an alkaline solution after drying andexposure, the unexposed parts of the photosensitive prepolymer are morepoorly soluble owing to the presence of the epoxy compound. Moreover,the epoxy compound frequently reacts with the epoxide curing agent asearly as during the drying step, which slows down the development andleads to a poorly developable layer on the copper surface.

U.S. Pat. No. 4,438,189 describes a composition compriseing a compoundwhich comprises at least two terminal ethylenically unsaturated groups,a curing agent, a photocurable prepolymer and a compound which isheat-curable.

EP 0 323 563 describes a resin composition compriseing photosensitiveprepolymer, a photoinitiator, a photopolymerizable vinyl monomer and/ora solvent and a finely pulverulent epoxy compound.

WO 94/03545 describes a composition as a coating material for metal andwood surfaces, compriseing a curing agent having a free carboxylic acid,a compound having a β-hydroxyalkylamido group and a polyester resin.

It has now surprisingly been found that outstanding curing and hencealso excellent resistance to solvents can be achieved and crosslinkingduring drying can be substantially avoided if a thermally crosslinkableprepolymer compriseing acid groups is mixed withN-hydroxyalkyl-substituted carboxamides. Surprisingly, it was found thatsuch a composition crosslinks extremely well at temperatures above 150°C. and thus forms layers which are resistant to solvents.

The invention relates to a composition having the features of claim 1.Further advantageous embodiments of the invention are evident from thedependent claims and the description.

The composition comprises a compound of the formula (I),

in which

-   A is a mono- to tetravalent, saturated, or unsaturated alkyl group    having 1 to 60, preferably 1 to 20 and in particular 2 to 10 carbon    atoms, such as, for example, ethyl, methyl, propyl, butyl, pentyl,    hexyl, heptyl, octyl, nonyl, decyl, eicosyl, tricontyl, tetracontyl,    pentacontyl or hexacontyl, a mono- to tetravalent aryl group, such    as, for example, phenyl or naphthyl, a mono- or dialkylamino group    having 1 to 4 carbon atoms, a mono- or di(hydroxyalkyl)amino group    having 2 to 4 carbon atoms, such as, for example, dimethylamine,    ethylamine or hydroxyethylamine, a mono- to tetravalent alkenyl    group having 2 to 4 carbon atoms, such as, for example, ethenyl,    1-methylethenyl, 3-butene-1,3-diyl and 2-propene-1,2-diyl,    carboxyalkyl or carboxyalkenyl groups, such as 3-carboxy-2-propenyl    groups, alkoxycarbonylalkyl or alkoxycarbonylalkenyl groups having 1    to 4 carbon atoms, such as, for example,    3-methoxycarbonyl-2-propenyl groups,-   R¹ is hydrogen, an alkyl group or a hydroxyalkyl group having 1 to 5    carbon atoms (such as, for example, methyl, ethyl, n-propyl,    n-butyl, sec-butyl, tert-butyl or pentyl, 2-hydroxyethyl,    3-hydroxypropyl, 2-hydroxypropyl, 4-hydroxybutyl, 3-hydroxybutyl or    2-hydroxy-2-methylpropyl) and-   n is 1 or 2, m is 2-n and q is a number from 0 to 3,-   X is a radical of the formula    in which R³ and R⁴ are identical or different and each radical,    independently of one another, is hydrogen or straight-chain or    branched alkyl having 1 to 5 carbon atoms or R³ and R⁴, together    with the carbon atom to which they are bonded, form a cycloaliphatic    ring (such as, for example, cyclopentyl or cyclohexyl), or are a    hydroxyalkyl group having 1 to 5 carbon atoms (hydroxymethyl and    1-hydroxyethyl).

Particularly preferably, n is 2 and m is 0. A is preferablyC₂-C₁₀-alkylene and particularly preferably C₂-C₈-alkylene, which may belinear or branched.

The composition according to the invention particularly preferablycomprises a compound of the formula II,

in which R⁴ is as defined above and is preferably hydrogen or methyl.These compounds are solid at 120° C. and become liquid at temperaturesabove 150° C.

In a further preferred embodiment, the compound of the formula I is aliquid bi- to tetrafunctional compound having a viscosity of 1 000-10000 mPa·s at 25° C. Primid V 40-30 is particularly preferred.

The at least bifunctional acidic prepolymer (A) curable by the action ofheat is preferably selected from the group consisting of the acrylateresins, polyurethane resins, the cyanate ester resins, the benzoxazineresins, the polyphenylene resins, the polyimide resins and mixturesthereof.

The composition according to the invention preferably comprises from 3to 50% by weight, particularly preferably from 5 to 35% by weight and inparticular from 8 to 20% by weight of the compounds of the formula I andfrom 97 to 50% by weight, particularly preferably from 95 to 65% byweight and in particular from 92 to 80% by weight, of a curable, atleast bifunctional acidic prepolymer (A), based on the compositioncompriseing the two components.

In a particularly preferred embodiment, the composition according to theinvention comprises an acidic prepolymer (A) which is both photocurableand heat-curable. This is preferably selected from the group consistingof:

-   -   a photocurable and heat-curable acidic prepolymer having an acid        value of from 40 to 250 mg KOH/g, obtainable by reacting a        polymer or copolymer compriseing unsaturated carboxyl groups        with a compound which comprises an alicyclic epoxy group;    -   a photocurable and heat-curable acidic prepolymer, obtainable by        complete esterification of the epoxy groups of an epoxy resin        with an α,β-unsaturated carboxylic acid and subsequent reaction        of the product thus obtained with a saturated or unsaturated        carboxylic anhydride;    -   a photocurable and heat-curable acidic prepolymer, obtainable by        reaction of a bisphenol A type epoxy compound with        epichlorohydrin with formation of a post-glycidylated epoxy        compound, subsequent complete esterification of the epoxy groups        of the post-glycidylated epoxy compound with an α,β-unsaturated        carboxylic acid and subsequent reaction of the product obtained        with a saturated or unsaturated carboxylic anhydride, and    -   a photocurable and heat-curable acidic prepolymer, obtainable by        reaction of a bisphenol A type epoxy compound with        epichlorohydrin with formation of a post-glycidylated epoxy        compound, mixing of the post-glycidylated epoxy compound with a        novolak epoxy compound, complete esterification of the mixture        with an α,β-unsaturated carboxylic acid and subsequent reaction        of the product thus obtained with a saturated or unsaturated        carboxylic anhydride.

These photocurable and heat-curable acidic prepolymers (A) may bepresent alone or as mixtures in the composition according to theinvention.

The abovementioned unsaturated monobasic acid copolymer resins areobtainable by copolymerizing an ethylenically unsaturated carboxylicacid, such as, for example, (meth)acrylic acid, 2-carboxyethyl(meth)acrylate, 2-carboxypropyl (meth)acrylate, maleic anhydride and thelike, with at least one monomer selected from the group consisting of(meth)acrylic esters, such as methyl (meth)acrylate, ethyl(meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate,2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, hydroxyethyl(meth)acrylate, hydroxypropyl (meth)acrylate and the like; vinylaromaticcompounds, such as styrene, α-methylstyrene, vinyltoluene,p-chlorostyrene and the like; amide-like unsaturated compounds, such as(meth)acrylamide, diacetoneacrylamide, N-methylolacrylamide,N-butoxymethylacrylamide and the like; polyolefin compounds, butadiene,isoprene, chloroprene and the like; and other compounds, such as(meth)acrylonitrile, methyl isopropenyl ketone, vinyl acetate, Beobamonomer (product of Shell Chemical), vinyl propionate, vinyl pivalateand the like. The acid value of the unsaturated copolymer is preferablyin the range from 30 to 260 mg KOH/g.

The unsaturated compound compriseing an alicyclic epoxy group is acompound having an unsaturated group capable of free radicalpolymerization and an alicyclic epoxy group in one molecule. Thisunsaturated compound compriseing an alicyclic epoxy group is obtainableby copolymerization of an unsaturated monomer as a main monomercomponent compriseing an alicyclic epoxy group with at least oneabove-described monomer of the unsaturated monobasic acid copolymerresins, such as a (meth)acrylic ester, vinylaromatic compounds and thelike.

For the preparation of the radiation-curable and photocurable acidicprepolymer from an unsaturated resin compriseing an alicyclic epoxygroup and an unsaturated compound compriseing an acid group, a solutionof an unsaturated resin compriseing an alicyclic epoxy group in an inertorganic solvent is reacted with the unsaturated compound compriseing theacid group for from 1 to 7 hours at a temperature of from 20 to 110° C.

The radiation-curable and photocurable acid-compriseing prepolymer thusobtained has from 0.2 to 4.0, preferably from 0.7 to 3.5, double bondsper 1 000 molecular weight units and an average molecular weight of from1 000 to 100 000 g/mol, preferably from 3 000 to 20 000 g/mol.

The following general formula (III) shows a photocurable andheat-curable acidic prepolymer (A)

which is particularly preferably present in the composition according tothe invention and in which

-   R⁵ is hydrogen or a methyl group,-   R⁶ is a divalent aliphatic saturated hydrocarbon group having 1 to    14 carbon atoms and in particular a linear or branched alkylene    chain, such as methylene, ethylene, propylene, tetramethylene,    ethylethylene, pentamethylene or hexamethylene, or a phenylene,-   R¹⁰, R¹¹ and R¹², independently of one another, are hydrogen or a    methyl group,-   Z is a direct bond or a divalent cycloalkane having 5 to 10 carbon    atoms,-   a and b are numbers from 1 to 10 and c is a number from 0 to 10.

In the resin composition according to the invention, the ratio a:b:c ispreferably 5:3:2. The acid value is preferably in the range of 60-90 mgKOH/g, since the composition is most stable and has the best propertiesin this range. The molecular weight is preferably in the range from400-6 000 g/mol.

For the preparation of an acidic prepolymer which is curable by theaction of heat and photocurable from an acrylic resin compriseing anacid group and an unsaturated compound compriseing an alicyclic epoxygroup, for example, a solution of an acrylic resin compriseing an acidgroup in an inert organic solvent, such as alcohol, ester, aromatichydrocarbons and the like, can be reacted with the unsaturated compoundcompriseing the alicyclic epoxy group at a temperature of from 20 to120° C. for from 1 to 5 hours.

The acidic prepolymer preferably comprises from 0.2 to 4.0, particularlypreferably from 0.7 to 3.7, double bonds per 100 g/mol molecular weight.If the number of double bonds is in this range, good curing is achievedand the adhesive properties with respect to the substrate and theresistance to water are ideal.

The photocurable and heat-curable acidic prepolymers preferably have anaverage molecular weight from 1 000 to 100 000 g/mol, particularlypreferably from 3 000 to 70 000 g/mol. With these molecular weights, thephotocurable acid-compriseing prepolymer can be readily used owing toits viscosity.

The acid value of the photocurable and heat-curable acidic prepolymer ispreferably up to 120 mg KOH/g, since the composition according to theinvention then has good water resistance.

Alternatively, photocurable and heat-curable acidic prepolymer which isobtainable by reacting a vinyl resin compriseing an alicyclic epoxygroup and an unsaturated compound compriseing an acid group may also bepresent in the composition according to the invention.

The abovementioned photocurable and heat-curable resins may be presentalone or in combination in the composition according to the invention.

In a further preferred embodiment, the composition according to theinvention comprises, as acidic prepolymer (A) which is both curable bythe action of heat and radiation-curable, the prepolymer of the formulaIV, which has been reacted with a dicarboxylic anhydride, for examplephthalic anhydride,

in which s is a number from 1 to 20.

The formulation according to the invention may also comprise aprepolymer (B) which is only photocurable.

The composition according to the invention has excellentphotosensitivity. The compound of the formula I does not adverselyinfluence the development process, and no gelling occurs. Consequently,the composition according to the invention can be rapidly developed. Inthe subsequent thermal step, the compound of the formula I is melted,unless it is already present in the liquid state, and is reacted withthe photocurable and heat-curable acid-compriseing prepolymer. Thisgives a layer, such as, for example, a solder resist mask for circuitboards, which meets the abovementioned requirements.

In a further preferred embodiment, the formulation according to theinvention additionally comprises a telechelic elastomer and/or aparticulate material having a core and a shell, the core compriseing asilicone resin and the shell an acrylate resin. The telechelic elastomerhas at least one primary hydroxyl group at one end of the molecule andhas at least one epoxidized polyisoprene group at the other end of themolecule. A particularly preferred telechelic elastomer is the KratonLiquid EKP-207 polymer. A particularly preferred particulate materialhaving a core and a shell is Silicone Core Shell (Wacker AG, Germany). Alayer produced using such a formulation is extremely resistant to rapidtemperature changes.

A diluent, which is a photopolymerizable vinyl monomer and/or an organicsolvent, is preferably added to the composition according to theinvention.

The photopolymerizable vinyl monomers are preferably selected from thegroup consisting of hydroxyalkyl acrylates, such as 2-hydroxyethylacrylate, 2-hydroxybutyl acrylate and the like; mono- or diacrylates ofglycol, such as ethylene glycol, methoxytetraethylene glycol,polyethylene glycol, propylene glycol and the like, ethylene glycoldiacrylate, diethylene glycol diacrylate and the like; acrylamides, suchas N,N-dimethylacrylamide, N-methylolacrylamide, methylenebisacrylamide,diethylenetriaminetriacrylamide, bisacrylamidopropoxyethane,bismethacrylamidoethyl methacrylate,N-[(β-hydroxyethyloxy)ethyl]acrylamide and the like; aminoalkylacrylates, such as N,N-dimethylaminoethyl acrylate and the like;polyvalent acrylates of polyols, such as hexanetriol,trimethylolpropane, pentaerythritol, dipentaerythritol, trihydroxyethylisocyanurate and the like, and ethylene oxide adducts thereof orpropylene oxide adducts; phenoxyacrylates, bisphenol A diacrylate andacrylates of ethylene oxide adducts and propylene oxide adducts of thesephenols; acrylates of glycidyl ethers, such as glyceryl diglycidylether, trimethylolpropane triglycidyl ether, triglycidyl isocyanurateand the like; melamine acrylate; and methacrylates of the abovementionedacrylates; etc.

The organic solvents are preferably selected from the group consistingof the ketones, such as methyl ethyl ketone, cyclohexanone and the like;aromatic hydrocarbons, such as toluene, xylene, tetramethylbenzene andthe like; glycol ethers, such as methylcellosolve, butylcellosolve,methylcarbitol, butylcarbitol, propylene glycol monomethyl ether,dipropylene glycol monoethyl ether, triethylene glycol monoethyl etherand the like; esters, such as ethyl acetate, butyl acetate, acetates ofthe abovementioned glycol ethers and the like; alcohols, such asethanol, propanol, ethylene glycol, propylene glycol and the like;aliphatic hydrocarbons, such as octane, decane and the like; andpetroleum solvents, such as petroleum ether, petroleum naphtha,hydrogenated petroleum naphtha, naphtha solvents and the like. Theseorganic solvents serve for reducing the viscosity of the compositionaccording to the invention, which leads to an improvement in itsapplication properties.

The diluent may be used alone or as a mixture of a plurality ofdiluents. The composition according to the invention expedientlycomprises up to 15% by weight of the diluent, based on the compositionaccording to the invention.

By adding the photopolymerizable vinyl monomer as a diluent, not only isthe viscosity reduced but at the same time the photopolymerizabon rateis increased.

The photopolymerization initiator may also be added to the compositionaccording to the invention if the composition is cured by UV exposure.Typical examples of photopolymerization initiators are benzoin andbenzoin alkyl ethers, such as benzoin, benzil, benzoin methyl ether,benzoin ethyl ether, benzoin n-propyl ether, benzoin n-butyl ether,benzoin isopropyl ether and the like; benzophenones, such asbenzophenone, p-methylbenzophenone, Michler's ketone,methylbenzophenone, 4,4′-dichlorobenzophenone,4,4-bisdiethylaminobenzophenone and the like; acetophenones, such asacetophenone, 2,2-dimethoxy-2-phenylacetophenone,2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone,1-hydroxycyclohexyl phenyl ketone,2-methyl[4-(methylthio)pheny]-2-morpholino-1-propanone,N,N-dimethylaminoacetophenone, and the like; thioxanthone and xanthones,such as 2,4 dimethylthioloxanthone, 2,4-diethylthioxanthone,2-clhorothioxanthone, 2,4-diisopropylthioxanthone and the like;anthraquinones, such as anthraquinone, chloroanthraquinone,2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone,1-chloroanthraquinone, 2-amylanthraquinone, 2-aminoanthraquinone and thelike; ketals, such as acetophenone dimethyl ketal, benzyl dimethyl ketaland the like; benzoic esters, such as ethyl 4-dimethylaminobenzoate,2-dimethylamino)ethyl benzoate, ethyl-dimethylaminobenzoate and thelike; phenyl disulphides, 2-nitrofluorene, butyloin, anisoin ethylether, azobisisobutyronltriles, tetramethylthiuram disulphide and thelike. These compounds may be present individually or in combination inthe composition according to the invention.

The photopolymerization initiator is preferably present in an amount offrom 0.1 to 10 percent by weight, based on the composition according tothe invention.

The composition according to the invention may also comprise inorganicand/or organic fillers in order to improve the adhesion properties orthe hardness of the layer. The inorganic fillers are preferably selectedfrom the group consisting of barium sulphate, barium titanate,pulverized silica, finely pulverized silica, amorphous silica, talc,chalk, magnesium carbonate, calcium carbonate, alumina, aluminiumhydroxide, mica powder and the like. The composition according to theinvention comprises up to 40 percent by weight, preferably 5-30 percentby weight, of inorganic fillers, based on the composition according tothe invention.

The composition according to the invention may also comprise additives,such as colorants, thickeners, antifoams, levelling agents, thermalpolymerizabon inhibitors or antioxidants. Possible colorants arephthalocyanine blue, phthalocyanine green, iodine green, disazo yellow,crystal violet, titanium oxide, carbon black, naphthalene black and thelike. Possible thermal polymerization inhibitors are hydroquinone,hydroquinone monomethyl ether, tert-butylcatechol, pyrogallol,phenothiazine and the like. Suitable thickeners are, for example,orbene, bentone, montmorillonite and the like. Suitable antifoams are,for example, fluorosilicone-like, fluoride-like or polymer-likeantifoams.

In the production of a circuit board compriseing a layer, such as, forexample, a solder resist mask, the printed circuit board is first coatedwith the composition according to the invention and then dried forevaporation of the diluent with formation of a layer (from 60 to 90° C.for from 15 to 60 minutes). This layer is then selectively exposed,preferably with the use of a patterned negative mask. After theexposure, the layer is developed with a developing liquid in order toremove the unexposed parts of the layer. Finally, the layer is postcuredby heating, a solder resist mask serving as protective layer beingobtained on the circuit board. The heat treatment for the postcuring canbe carried out at from 100 to 160° C., preferably from 130 to 180° C.

Electronic components compriseing a layer produced using the formulationaccording to the invention are stable for a long time. One-layer ormultilayer circuit boards compriseing at least one layer produced usingthe composition according to the invention are particularly preferred.

The formulation according to the invention is preferably sold in a setcompriseing two compriseers A and B. Those components which reacttogether are separated, so that the compriseer A comprises the compoundof the formula I and the compriseer B comprises the remainingcomponents, such as the acid-compriseing prepolymer curable under theaction of heat and optionally the photocurable acid-compriseingprepolymer, the photopolymerization initiator and/or fillers.

The following examples explain the invention in more detail. Parts areparts by weight.

EXAMPLE 1 A Photocurable Acid-Compriseing Prepolymer

A mixture consisting of 20 parts of methyl methacrylate, 20 parts ofstyrene, 25 parts of methyl acrylate, 15 parts of 2-hydroxyethylmethacrylate, 20 parts of acrylic acid and 5 parts ofazobisisobutyronitrile is added dropwise to 60 parts of butylcellosolve,which is initially introduced into a reactor, in a nitrogen atmosphereover a period of 3 hours. After the addition, the resulting mixturereacts for a further hour. Thereafter, a mixture consisting of 1 part ofazobisdimethylvaleronitrile and 7 parts of butylcellosolve is added overa period of one hour and the resulting mixture in turn is reacted for 5hours. The resin thus formed has a high acid value (150). After additionof 25 parts of an unsaturated resin having an alicyclid epoxy group and0.06 part of hydroquinone, the resulting mixture is reacted at 80° C.for 5 hours with addition of air. The photocurable prepolymer thusobtained has an acid value of 60 and an average molecular weight of 10000 g/mol.

EXAMPLE 2

The glycidation of a side chain of an epoxy resin can be carried out byknown methods as described, for example, in JP-A-8-134390. 100 parts ofa bisphenol A type epoxy resin (GT7004, produced by Vantico; softeningpoint 101° C., epoxide equivalent =730, average molecular weight 1 460,n=3.9 on average) are dissolved in a mixture of 171 parts ofepichlorohydrin and 116 parts of dimethyl sulphoxide. 15 parts of 98.5%NaOH are added dropwise at 70° C. to this solution over a period of 100minutes. After the addition, the reaction is carried out in a period of3 hours at 70° C. The main part of the excess unreacted epichlorohydrinand of the dimethyl sulphoxide is then distilled off under reducedpressure. The reaction product contaminated with dimethyl sulphoxide andthe salt formed as a byproduct are dissolved in 187.5 parts of methylisobutyl ketone. 1.8 parts of 30% NaOH are added to this solution andreaction is effected at 70° C. for 1 hour. After the reaction, thereaction mixture is washed with 50 parts of water. After the organicphase has been separated from the aqueous phase, the isobutyl ketone isdistilled off from the organic phase in order to obtain 81.2 parts of anepoxy resin having an epoxide equivalent of 305 and a softening point of83° C. In the epoxy resin, 3.5 mol out of 3.9 mol of the alcoholic OHgroups have been epoxidized.

EXAMPLE 3

In a three-necked flask having a stirrer and a condenser, 1.09 parts ofa cresol novolak type epoxy resin having an epoxide equivalent of 215(JDCN-702, produced by Tohto Kasei AG) are heated and are melted at90-100° C. while stirring. 390 parts of acrylic acid, 1 part ofhydroquinone and 2 parts of benzyldimethylamine are then added. Themixture is heated to 110-115° C. and reacted for 12 hours whilestirring. The solution thus obtained is then cooled to room temperature.The resulting product of a novolak type epoxy compound in which theacrylic acid is completely esterified has an acid value of 3 mg KOH/g.450 parts of this product are introduced, together with 125 parts ofethylcarbitol acetate and 125 parts of Solvesso #150, into a reactor andstirred at 70-80° C. so that a homogeneous solution forms. One hydroxylequivalent of the resulting solution is then reacted with 0.5 mol oftetrahydrophthalic anhydride. A solution of the acid anhydride adducthaving an acid value of 58 mg KOH/g is obtained.

The compositions are prepared according to the ratios shown in table 1.The numerical values are stated in % by weight. After an initial briefmixing of the ingredients, each formulation is kneaded twice in athree-roll mill. The size distribution of the particles in eachformulation is measured using a grindometer (produced by Erichsen Co.).The particles thus obtained are smaller than 16 μm.

The total surface area of a circuit board is coated with the compositionand dried in an air circulation oven at 80° C. for 20 minutes. Afterdrying, the layer thus obtained is exposed to light, developed andfinally cured by heat in order to obtain a solder resist pattern.

Resistance to Hot/Cold Cycles

Each formulation is exposed through a photomask to ultraviolet light ata wavelength of 365 nm and in a dose of 200-400 mJ/cm² (measured usingan integral actinometer produced by Oak Selsakusho AG). The developmentis carried out with a weakly aqueous alkaline developing solution for 60seconds under a spray pressure of 2 kg/cm². The developed test board isplaced in an apparatus for temperature change. The temperature ischanged alternately from −55° C. to 125° C., the temperature beingmaintained in each case for 15 minutes. The term cycle is used when thetemperature change from −55° C. to 125° C. (or back) is complete. Theformation of new tears is checked after 50 cycles. If a tear is found,the test is terminated.

Photosensitivity Test

Each test board is exposed to ultraviolet light at a wavelength of 365nm and in a dose of 300 mJ/cm², 400 mJ/cm² and 450 mJ/cm² (measuredusing an integral actinometer (Oak Seisakosho AG)). After thedevelopment with a weakly alkaline aqueous solution for 60 seconds undera gentle spray pressure of 2 kg/cm², the state of the film thus formedis checked visually and assessed according to the following criteria:

-   Q: no change observable-   R: slight change observable-   S: slight change of surface observable-   T: the film is tom off.    Development Test

The test board is prepared by exposure of the coated test board througha photomask to ultraviolet light having a wavelength of 365 nm and in adose of 200-400 mJ/cm² (measured using an integral actinometer (OakSeisakosho AG)). In the comparative examples, exposure is effected usinga dose of 200-750 mJ/cm². The development is carried out in a weaklyalkaline aqueous solution under a spray pressure of 2 kg/cm² for aperiod of 20, 40 or 60 seconds. After the development, the removal ofthe unexposed layer is checked visually and assessed according to thefollowing criteria:

-   Q: complete development was achieved-   R: a thin layer of undeveloped material remains on the surface-   S: undeveloped material is distributed over the entire test board-   T: scarcely any development was achieved.    Adhesion Test (According to DIN 53151)

The test board is exposed through a photomask to ultraviolet light at awavelength of 365 nm and in a dose of 200400 mJ/cm² (measured using anintegral actinometer (Oak Seisakosho AG)). In the comparative examples,exposure is effected at a dose of from 200 to 750 mJ/cm². Thedevelopment is carried out with a weakly alkaline aqueous solution undera spray pressure of 2 kg/cm² for a period of 60 seconds. The developedtest boards are postcured under various conditions. Each test board thusobtained is subjected to a crosshatch test and subjected to a peel testwith a cellophane adhesive tape. The test boards are then checkedvisually and the result is assessed according to the following criteria:

-   Q: 100/100 no peeling observable-   R: 100/100 slight peeling in the crosshatch lines-   S: 50/100 to 90/100 moderate adhesion-   T: 0/100 to 50/100 weak adhesion.    Pencil Hardness Test

The same test board used in the adhesion test is subjected to a hardnesstest by the method of JISK5400 under a load of 1 kg.

Acid Resistance Test

The same test board which is used in the adhesion test is placed in a10% (V/V) aqueous sulphuric acid solution at 20° C. for 30 minutes. Theacid resistance is assessed on the basis of the peeling and of theadhesion:

-   Q: no change observable-   R: slight change observable-   S: considerable change observable-   T: swelling of the film or falling off of the film as a result of    swelling observable.    Alkali Resistance Test

The test and the assessment are carried out analogously to the acidresistance test, except that the aqueous sulphuric acid solution isreplaced by a 10% by weight aqueous NaOH solution.

Solvent Resistance

The test and the assessment are carried out analogously to the addresistance test, except that the aqueous sulphuric acid is replaced byacetone.

Metallization Stability Test (Ni/Au stability)

The plating solution used is Aotolonex Cl (plating solution produced byCellex Corp. USA). The test board used is the same as that used in theadhesion test. This is metallized for 9 minutes at a liquid temperatureof 30° C. and a current density of 1 A/dm², in order to apply gold in athickness of 1.5 μm. The condition of the film is assessed under thesame criteria as for the acid resistance test.

Solder Resistance Test

According to the test methods described in JISC6481, the test board usedin the adhesion test is immersed for 10 seconds in a solder bath at 260°C. (once on one side and 3 times on the other side). The condition ofthe film is then checked according to the same criteria as in the acidresistance test.

Sensitivity

A film of a sample is exposed to ultraviolet light at a wavelength of365 nm and in a dose of 200-400 mJ/cm² (measured using an integralactinometer (Oak Seisakosho AG)) and then developed in a weakly alkalineaqueous solution under a spray pressure of 2 kg/cm² for 60 seconds.After the development, the film is checked visually. The photomask usedis a Step-Tablet, produced by Stoffer Co. In the case of the test boardsthus obtained, the tack/dryness after drying, the photosensitivity, thedevelopability (condition of the film after development), flexibilityafter final curing, cold/hot stability, adhesion, hardness of the film,acid resistance, alkali resistance, solvent resistance, metallizationstability, solder heat resistance, flux resistance, insulationresistance, insulabon resistance under humid conditions, resolution,water absorption and sensitivity are assessed. The results aresummarized in table 2. The test boards of the comparative examples areexposed at 750 mJ/cm² since the surface of the resist is damaged and thecharacteristic properties cannot be compared with those exposed at 300mJ/cm².

Stability of the Formulation After Mixing

The ingredients of the composition are combined. After initial briefmixing of the ingredients, each formulation is kneaded twice in athree-roll mill. The formulation is stored at 40° C. The stability ofthe formulation is checked daily.

Stability After Coating

The formulation is applied as described above to the surface of acircuit board. The coated circuit board is not further processeddirectly but is stored and further processed later on. TABLE 1Formulations Example No. 1 2 3 4 5 6 7 8 Resin 40.6 24.13 44.04according to example 1 Resin 40.88 43.77 44.26 according to example 2Resin 39.34 14.67 39.78 according to example 3 Irgacure ® 6.83 6.84 6.907.02 6.18 6.22 6.25 8.93 907 Quantacure ® 0.97 0.97 0.39 0.39 1.05 1.060.40 ITX Sartomer ® 2.93 3.04 2.96 351 Sartomer ® 9.95 10.03 8.16 8.467.15 6.44 10.85 8.25 399 Barium 24.38 23.12 25.62 25.26 24.97 33.3625.26 25.89 sulphate Flowlen AC 0.31 0.31 — — 0.33 0.34 0.34 303 TSA — —2.02 1.99 750 S ® Disperbyl ® 0.08 0.08 0.07 0.07 0.09 0.09 0.09 0.09170 Phthalocyanine 0.44 0.44 0.54 0.56 0.48 0.48 0.48 0.54 green PrimidXL 552 6.81 6.04 5.39 6.06 6.47 Primid ® 5.90 5.42 4.35 V 40-30Particulate 5.02 material having a core and shell (silicone core shell)Kraton L 207 1.50

TABLE 2 Comparison of the properties Example No. 1 2 3 4 5 6 7 8Developability Q Q Q Q Q Q R Q Photosensitivity Q Q Q Q Q Q Q Q Adhesionin 0 0 0 0 0 4 0 4 crosshatch test Pencil hardness 6H 6H 6H 6H 4H 5H 7H6H Punching behaviour moderate moderate good moderate good poor moderatepoor Acid resistance Q Q Q Q Q Q Q Q Alkali resistance Q Q Q Q Q T S SSolvent resistance R R R R R S S S Solder resistance Q Q Q Q Q Q Q QNi/Au stability R Q Q R Q T T T Resistance to <50 <50 <50 <50 >700 <50<50 <50 hot/cold cycles cycles cycles cycles cycles cycles cycles cyclescycles  −55° C./15 min +165° C./15 min Hold timeafter >7d >7d >7d >7d >7d >7d >1d >7d coating Stability at 40°C. >12W >12W >12W >12W >12W >12W <1d >12W

1. A composition compriseing an at least bifunctional acidic prepolymer(A) curable under the action of heat, which additionally comprises acompound of the formula I

in which A is a mono- to tetravalent, saturated or unsaturated alkylgroup having 1 to 60 carbon atoms, a mono- to tetravalent aryl group, amono- or dialkylamino group having 1 to 4 carbon atoms, an alkenylenegroup having 2 to 4 carbon atoms, a carboxyalkylene group or analkoxycarbonylalkylene group having 1 to 4 carbon atoms in the alkylenegroup, n is 1 or 2, m is 2-n, q is a number from 0 to 3, R¹ is hydrogenor an alkyl group having 1 to 5 carbon atoms or a hydroxyalkyl grouphaving 1 to 5 carbon atoms and X is a radical of the formula

in which R³ and R⁴ are identical or different and, independently of oneanother, are hydrogen, a straight-chain or branched alkyl group orhydroxyalkyl group having 1 to 5 carbon atoms, or R³ and R⁴, togetherwith the carbon atom to which they are bonded, form a cycloaliphaticring.
 2. A composition according to claim 1, compriseing, as thecompound of the formula I, the compound of the formula II

in which R⁴ in each case is hydrogen or in each case is a methyl group.3. A composition according to claim 1, wherein the acidic prepolymer (A)is both heat-curable and photocurable.
 4. A composition according toclaim 1, which additionally comprises a photocurable prepolymer (B). 5.A composition according to claim 3 or claim 4, which additionallycomprises a photopolymerization initiator.
 6. A composition according toclaim 1, which additionally comprises fillers.
 7. A compositionaccording to claim 2, wherein, in the compound of the formula II, R⁴ isin each case hydrogen.
 8. A composition according to claim 2, wherein,in the compound of the formula II, R⁴ is in each case a methyl group. 9.A composition according to claim 1, wherein the acidic prepolymer (A) isa prepolymer of the formula III

in which R⁵ is hydrogen or a methyl group, R⁶ is a linear or branchedalkylene chain having 1 to 14 carbon atoms, R¹⁰, R¹¹ and R¹²,independently of one another, are hydrogen or a methyl group, Z is adirect bond or cycloalkylene having 5 to 10 carbon atoms, a and b are anumber from 1 to 10 and c is a number from 0 to
 10. 10. A compositionaccording to claim 1, wherein the acidic prepolymer (A) is one which isobtainable by reacting a prepolymer of the formula IV with adicarboxylic anhydride

in which s is a number from 1 to 20 and the acidic prepolymer (A) iscurable both by the action of heat and by exposure to light.
 11. Acomposition according to claim 1, which additionally comprises atelechelic elastomer and/or a particulate material having a core and ashell, the core compriseing a silicone resin and the shell an acrylateresin.
 12. A printed circuit compriseing layer produced from thecomposition of claim
 1. 13. A printed circuit according to claim 12,which is a circuit board.
 14. A packaging unit compriseing twocontainers A and B, which together compromise the composition accordingto claim 1, wherein the container A comprises the compound of theformula I; and the container B comprises the at least bifunctionalacidic prepolymer (A) curable under the action of heat and optionallyone or more components selected from the group consisting of aphotocurable prepolymer (B), a photopolymerization initiator, andfillers.
 15. (canceled)
 16. A process for the production of a circuitboard compriseing the steps of forming a layer of the composition ofclaim 1 on the circuit board, and post-curing the layer.
 17. The processof claim 16, further compriseing after formation of the layer, the stepof drying the layer.
 18. The process of claim 17, wherein the dryingstep is carried out at 60 to 90° C. and from 15 to 60 minutes.
 19. Theprocess of claim 16, further compriseing after the step of forming thelayer, the steps of selectively exposing the layer and removingunexposed parts of the layer.
 20. The process of claim 19, wherein thestep of selectively exposing the layer is carried out with the use of apatterned negative mask.
 21. The process of claim 19, wherein the stepof removing unexposed parts of the layer is carried out by developingthe layer with a developing liquid.
 22. The process of claim 16, whereinthe post-cure step is performed with heat treatment in the range from100 to 160° C.
 23. The process of claim 22, wherein the heat treatmentis in the range from 130 to 180° C.